The present invention relates to a safety switch for operating a contact-bearing plunger.
In general, a safety switch includes a housing in which the contact-bearing plunger is mounted for spring-loaded to and fro motion by means of a rotatable switch wheel that is actuated by an actuator of particular configuration. The housing is formed with two lateral access openings for enabling selective insertion of the actuator to act upon the switch wheel. Arranged on both sides of the switch wheel are spring-loaded locking members which tend to bar a rotation of the switch wheel and release the switch wheel only after the actuator moves the locking members against the spring force to a release position.
Such safety switches are employed to cut a current supply, for example, when a protective cover is removed from an apparatus or a machine or when equipment doors are opened. In order to provide for such functional security, precautions should be undertaken to prevent unauthorized personnel or unintended operation of the switch by means of an actuator that can be simply copied or emulated and utilized. It is desirable that such safety switches be designed to be user-friendly and to minimize the number of models required, such that, for example, they can be accessed from two different sides because the manufacturer of such safety switches is not generally aware of the location and manner a safety switch ultimately will be installed.
German Pat. Nos. DE 31 00 862 C2, DE 33 30 109 C2 disclose safety switches of this general type, with the switch wheel being essentially divided into several sections. A center section cooperates with the contact-bearing plunger while lateral sections of the switch wheel can be displaced against a return spring force parallel to the axis of rotation of the switch wheel by means of an actuator that can be admitted through openings on two different sides of the housing, such that projections on the plunger which cooperate with stop faces on the lateral sections become disengaged from these stop faces. The switch wheel can thereby be rotated away from a middle position in one sense or the opposite sense by utilizing one access opening or the other for respectively actuating the switch.
As elements of the switch wheel itself assume locking functions and operate in two different directions, many degrees of freedom are required. Thus, the security of operation has room for improvement. Moreover, the displacement of the switch wheel sections involved in locking in a direction parallel to the axis of rotation of the switch wheel considerably increases the dimensions of such a safety switch.
Other safety switches of essentially comparable construction are known that are provided with locking members on both sides of the switch wheel or a control cam and move in a plane perpendicular to the axis of rotation of the switch wheel. A locking mechanism of this type includes highly complex gear trains with numerous parts that are expensive to produce and to assemble, and the use of rocker arms, pivot pins and similar parts makes them susceptible to outside forces. Furthermore, in such safety switches the locking members are laterally outside the switch wheel and are guided by the adjoining housing so that the access openings must be correspondingly wide. Security against manipulation is only two dimensional since e.g. both locking members can be operated by two screwdrivers, and an appropriate insertion leaves sufficient space for operating the switch wheel. Thus, despite the complicated construction, the security against manipulation needs also in this case further improvement.